Is contagion caused by local infectious spreaders or by a long-disance moving spreaders

How far can individuals move how large are populations

Is there inbreeding or are individuals freely outcrossing

3CASE STUDY

A grou

A stand of adjacent trees is infected by a disease How can we determine the way trees are infected? 4CASE STUDY

A grou

A stand of adjacent trees is infected by a disease How can we determine the way trees are infected? BY ANALYSING THE GENOTYPE OF THE MICROBES if the genotype is the same then we have local secondary tree-to-tree contagion. If all genotypes are different then primary infection caused by airborne spores is the likely cause of Contagion. 5CASE STUDY

A grou

WE HAVE DETERMINED AIRBORNE SPORES (PRIMARY INFECTION ) IS THE MOST COMMON FORM OF INFECTION QUESTION Are the infectious spores produced by a local spreader, or is there a general airborne population of spores that may come from far away ? HOW CAN WE ANSWER THIS QUESTION? 6If spores are produced by a local spreader..

Even if each tree is infected by different genotypes (each representing the result of meiosis like us here in this class).these genotypes will be related

HOW CAN WE DETERMINE IF THEY ARE RELATED?

7HOW CAN WE DETERMINE IF THEY ARE RELATED?

By using random genetic markers we find out the genetic similarity among these genotypes infecting adjacent trees is high

If all spores are generated by one individual

They should have the same mitochondrial genome

They should have one of two mating alleles

8WE DETERMINE INFECTIOUS SPORES ARE NOT RELATED

QUESTION HOW FAR ARE THEY COMING FROM? .or

HOW LARGE IS A POPULATION?

Very important question if we decide we want to wipe out an infectious disease we need to wipe out at least the areas corresponding to the population size, otherwise we will achieve no result.

9HOW TO DETERMINE WHETHER DIFFERENT SITES BELONG TO THE SAME POP OR NOT?

Sample the sites and run the genetic markers

If sites are very different

All individuals from each site will be in their own exclusive clade, if two sites are in the same clade maybe those two populations actually are linked (within reach)

In AMOVA analysis, amount of genetic variance among populations will be significant (if organism is sexual portion of variance among individuals will also be significant)

F statistics Fst will be over ) 0.10 (suggesting stongt structuring)

There will be isolation by distance

10Levels of Analyses

Individual

identifying parents offspring very important in zoological circles identify patterns of mating between individuals (polyandry, etc.)

In fungi, it is important to identify the "individual" -- determining clonal individuals from unique individuals that resulted from a single mating event.

Species variation among species what are the relationship between species.

Family, Order, ETC. higher level phylogenies

12What is Population Genetics?

About microevolution (evolution of species)

The study of the change of allele frequencies, genotype frequencies, and phenotype frequencies

13Goals of population genetics Natural selection (adaptation) Chance (random events) Mutations Climatic changes (population expansions and contractions) To provide an explanatory framework to describe the evolution of species, organisms, and their genome, due to Assumes that the same evolutionary forces acting within species (populations) should enable us to explain the differences we see between species evolution leads to change in gene frequencies within populations 14Pathogen Population Genetics

Random Genetic Drift if populations are small enough, by chance, sampling will result in a different allele frequency from one generation to the next.

18The smaller the sample, the greater the chance of deviation from an ideal population. Genetic drift at small population sizes often occurs as a result of two situations the bottleneck effect or the founder effect. 19(No Transcript) 20Founder Effects typical of exotic diseases

Establishment of a population by a few individuals can profoundly affect genetic variation

Consequences of Founder effects

Fewer alleles

Fixed alleles

Modified allele frequencies compared to source pop

GREATER THAN EXPECTED DIFFERENCES AMONG POPULATIONS BECAUSE POPULATIONS NOT IN EQUILIBRIUM (IF A BLONDE FOUNDS TOWN A AND A BRUNETTE FOUND TOWN B ANDF THERE IS NO MOVEMENT BETWEEN TOWNS, WE WILL ISTANTANEOUSLY OBSERVE POPULATION DIFFERENTIATION)

21(No Transcript) 22Bottleneck Effect

The bottleneck effect occurs when the numbers of individuals in a larger population are drastically reduced

By chance, some alleles may be overrepresented and others underrepresented among the survivors

Some alleles may be eliminated altogether

Genetic drift will continue to impact the gene pool until the population is large enough

23Founder vs Bottleneck 24Northern Elephant Seal Example of BottleneckHunted down to 20 individuals in 1890s Population has recovered to over 30,000 No genetic diversity at 20 loci 25Hardy Weinberg Equilibriumand F-Stats

In general, requires co-dominant marker system

Codominant expression of heterozygote phenotypes that differ from either homozygote phenotype.

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